EXCIMER-LASER CRYSTALLIZATION OF AMORPHOUS-SILICON FILMS

Excimer laser crystallized silicon films have been studied as a functi on of the number of laser shots, and the influence of the use of such polycrystalline films in Thin Film Transistors (TFTs) has also been in vestigated. It is found that electron mobility, one of the most import ant of all TFT characteristics, increases monotonically with the numbe r of irradiations, with maximum mobility being obtained at about 20 sh ots at the energy density of about 380 mJ/cm2. This result is not due to grain size, since transmission electron microscopy indicates that t he number of laser shots does not affect grain size, which is about 15 0 nm diameter, in polycrystalline silicon films. Raman studies and TFT carrier transport analysis, on the other hand, suggest that this incr ease in electron mobility may be explained by a decrease of defects, i ncluding small grains, grain boundaries and defects inside grains.